This lens is interesting because its not your typical set of concave and convex optical glass lenses in an aluminum tube. Instead, this lens relys on pair of catadioptric mirrors, much the same way a large astronomical telescope does.

For that reason, the lens is much smaller and much lighter than a refracting lens of the same focal length. For instance, I recently wrote about Nikon’s 400mm f/2.8 VR lens. You can see the humongous size of that lens here. This 500mm f/8 mirror lens is about 1/4 the length and 1/5 the weight of that monstrous 400mm f/2.8, so it is far more easily transportable. It also costs far less to produce, and therefore is MUCH less expensive to the consumer. A 400mm f/2.8 lens costs approximately $9,000, while this 500mm f/8 lens costs me a mere $150 on eBay.

There are downsides, though. This lens is all manual. The fancy autofocus or vibration reduction that exist on the bigger refracting lenses doesn’t exist here. Also, you’re limited to one stop, f/8, which makes this lens a bit tricky to use in lower-light situations. Fortunately, with the D3, I can crank the ISO up to 1000 (without worrying about image noise) and get shutter speeds in the range of 1/1000th to easily avoid motion blurr in my images.

Others have also complained about poor image quality (low contrast and soft focus), but my experience so far with the lens says that this lens can create images that are just as sharp and contrasty as other lenses. And with the help of software, there should be no issues.

Another thing about this lens that may or may not be a downer for you is the bokeh it produces. Instead of out-of-focus highlights being uniform balls of light, this lens produces ring-like highlights in out of focus areas due to the center, rear-facing mirror element. Depending upon who you are and what you shoot, this could be a boon or a hinderance. Personally, I think it produces an interesting effect.

All in all, I think this lens is a great addition to my bag of tricks. It’s very light and very small compared even to my 70-200mm f/2.8, and it will allow me to really reach out and grab an image at long distance. I forsee myself really using this for daylight wildlife images.

EDIT: I shot this image of the moon last night (8-30-09) with the reflex lens. At 1/500th of a second and ISO 500, this image came out perfectly-exposed, even though the camera’s exposure meter was pegged to the underexposed side. I used a tripod and the camera’s “mirror-up” function to minimize camera shake blur. It’s also a crop of the full frame. Pretty darned sharp, if you ask me.